1. Field of the Invention
The present invention relates generally to a ducted fan drive. More specifically, the present invention relates to a drive for counter rotating ducted fans which uses permanent magnets as an integral component of the drive system.
2. Description of the Prior Art
In the past, electric rotating machines included permanent magnet electric rotating machine, in which permanent magnets of the electric rotating machine are used as a magnetic field generating means for the rotor of the machine. In this type of rotating machines, plural permanent magnets of the electric rotating machine are arranged in parallel and fixed on a surface of the rotor and additional permanent magnets are arranged to have a reversed polarity at a peripheral direction.
Referring to FIGS. 1A and 1B, U.S. Pat. No. 6,208,054, which issued Mar. 27, 2001 to Fumio Tajima et al, discloses a prior art permanent magnet electric rotating machine, designated generally by the reference numeral 10. The invention of U.S. Pat. No. 6,208,054 comprises a permanent magnet electric rotating machine which includes a stator 11 and a rotor 12. As shown in FIG. 1A, the stator 11 and the rotor 12 are arranged with a rotation air gap formed between one another. The stator 11 is fixed to an inner peripheral surface of a housing 21 and a shaft 17, which is inserted in and fixed to the rotor 12, can rotate freely with a rotation air gap against the stator 11.
The stator 11 comprises a stator iron core 13 and a stator winding 14. The stator iron core 13 includes a core portion 15 and a stator salient pole portion 16. In the core portion 15, a magnetic circuit is formed so as to pass a magnetic flux to the stator salient pole portion 16. In this stator salient pole portion 16, the stator winding 14 is wound around in a concentrated manner. The rotor 12 includes a shaft 17, a rotor iron core 18 and a plurality of permanent magnets 19. In the rotor iron core 18, there are a plurality of permanent magnet insertion holes 20, in which are inserted the permanent magnets 19. The holes 20 for the permanent magnets 19 and the hole through which the shaft 17 passes punched out in an axial direction. The permanent magnets 19 are inserted in and fixed respectively to the permanent magnet insertion holes 20. The shaft 17 is inserted in and fixed to the shaft passing through hole.
By arranging the permanent magnets 19 around the rotor 12 in a ring-like form, a member formed between adjacent permanent magnet insertion holes 20 can function as an auxiliary magnetic pole 26. As shown in FIG. 1A, the permanent magnets 19 are arranged separately and equally around the circumference at the same distance in the respective permanent magnet insertion holes 20 of the rotor 12.
This allows a control apparatus (not shown in FIG. 1A) to control a composite force of an armature electromotive force according to the stator winding 14 so as to direct a force toward a side of a rotation direction but not direct a force toward a side of a central position direction of the auxiliary magnetic pole 26.
A magnetic flux generated from the stator winding 14 passes through the permanent magnets 19 and the auxiliary magnetic poles 16. A reluctant torque is then generated. This force is very effective in particular during a low speed operating condition of the permanent magnet electric rotating machine. Further, since the above stated reluctant torque is added to an ordinary torque provided by the permanent magnets 19, a high torque for the electric motor, is obtained.
Referring to FIG. 1B, there is shown an axial direction cross-sectional view of the prior art permanent magnet electric rotating machine of FIG. 1B. As shown in FIG. 1B, a magnetic gap 24 is provided between the permanent magnet 19 and the auxiliary magnetic pole portion 26, wherein the magnetic gap 24 is provided between the plurality of permanent magnets 19 and the auxiliary magnetic pole portions 16 to change the magnetic flux density of the permanent magnets 19 and the auxiliary magnetic pole portions 26 smoothly and to reduce cogging torque.